Methyl methacrylate polymerization at samarium(II)-grafted MCM-41

Sm(II)-modified periodic mesoporous silica (PMS), Sm[N(SiHMe₂)₂]₂(THF)_x@MCM-41, was used for the synthesis of Sm(II) alkyl, alkoxide, and indenyl surface species via secondary ligand exchange. The performance of the novel Sm(II)-based organometallic–inorganic hybrid materials as initiators for the graft polymerization of methyl methacrylate (MMA) is reported. All of the Sm(II) hybrid materials including the new PMMA–PMS composites were characterized via N₂ physisorption, elemental analysis, FTIR spectroscopy, and scanning electron microscopy (SEM). The organic–inorganic composites revealed complete pore blockage as well as enrichment and strong adhesion of the polymer at the exterior of the porous silica material.     

Adsorption, desorption, and surface-promoted hydrolysis of glucose-1-phosphate in aqueous goethite (α-FeOOH) suspensions

Adsorption, desorption, and precipitation reactions at environmental interfaces govern the fate of phosphorus in terrestrial and aquatic environments. Typically, a substantial part of the total pool of phosphorus consists of organophosphate, and in this study we have focused on the interactions between glucose-1-phosphate (G1P) and goethite (α-FeOOH) particles. The adsorption and surface-promoted hydrolysis reactions have been studied at room temperature as a function of pH, time, and total concentration of G1P by means of quantitative batch experiments in combination with infrared spectroscopy. A novel simultaneous infrared and potentiometric titration (SIPT) technique has also been used to study the rates and mechanisms of desorption of the surface complexes. The results have shown that G1P adsorption occurs over a wide pH interval and at pH values above the isoelectric point of goethite (IEP(goethite) = 9.4), indicating a comparatively strong interaction with the particle surfaces. As evidenced by IR spectroscopy, G1P formed pH-dependent surface complexes on goethite, and investigations of both adsorption and desorption processes were consistent with a model including three types of surface complexes. These complexes interact monodentately with surface Fe but differ in hydrogen bonding interactions via the auxiliary oxygens of the phosphate group. The apparent desorption rates were shown to be influenced by reaction pathways that include interconversion of surface species, which highlights the difficulty in determining the intrinsic desorption rates of individual surface complexes. Desorption results have also indicated that the molecular structures of surface complexes and the surface charge are two important determinants of G1P desorption rates. Finally, this study has shown that surface-promoted hydrolysis of G1P by goethite is base-catalyzed but that the extent of hydrolysis was small.     

Tetramethylcyclopentadienyl-supported rare-earth metal bis(tetramethyl)aluminate complexes: Synthesis,structural chemistry,cation formation,and isoprene polymerization

The protonolysis reaction of [Ln(AlMe₄)₃] with H(Cp′) (Cp′ = C₅Me₄H) gives access to half-sandwich complexes [(Cp′)Ln(AlMe₄)₂]. X-ray structure analyses of the samarium, neodymium, and lanthanum derivatives reveal a distinct [AlMe₄] coordination (one η², one bent η²) for the two smaller rare-earth metals. The lanthanum complex displays an unprecedented dimeric structure with two μ₂-η¹:η² coordinating [AlMe₄] ligands in the solid state. Treatment of complexes [(Cp′)Ln(AlMe₄)₂] with perfluorinated organoborates and -boranes produces discrete contact ion-pairs, which are characterized by ¹H, ¹³C, ²⁷Al, ¹⁹F, and ¹¹B NMR spectroscopy and act as efficient initiators for the fabrication of trans-1,4 polyisoprene. The polymerization performance is hereby affected by the rare-earth metal cation size, the type of boron cocatalyst, and the polymerization temperature.     

Electro-catalytic oxidative cleavage of lignin in a protic ionic liquid

Lignin is a component of lignocellulosic biomass and a promising matrix for recovering important renewable aromatic compounds. We present a new approach of electro-oxidative cleavage of lignin, dissolved in a special protic ionic liquid, using an anode with particular electro-catalytic activity. As appropriate ionic liquid triethylammonium methanesulfonate was identified, synthesised, explored for dissolution of alkali-lignin and used for electrolysis of 5 wt.% lignin solutions. As appropriate anode material, oxidation-stable ruthenium-vanadium-titanium mixed oxide electrodes were prepared and explored for their electro-catalytic activity. The electrolysis was performed at several potentials in the range from 1.0 V to 1.5 V (vs. an Ag pseudo reference electrode). A wide range of aromatic fragments was identified as cleavage products by means of GC-MS and HPLC measurements.     

Analysis of human brain tissue, brain tumors and tumor cells by infrared spectroscopic mapping

This study uses infrared (IR) spectroscopic, point detection, mapping procedures to examine tissue samples from normal brain specimens and from astrocytic gliomas, the most frequent human brain tumors. Model systems were derived from cultured glioma cell lines. IR spectra of normal tissue sections distinguished white matter from gray matter by increased spectral contributions from lipids and cholesterol. Qualitatively the same differences were found in IR spectra of low and high grade glioma tissue sections pointing to a significant reduction of brain lipids with increasing malignancy. Whereas spectral contributions of proteins and lipids were similar in IR spectra of glioma cells and tissues, nucleic acid bands were more intense for cells suggesting higher proliferative activities. For statistical analyses of IR spectroscopic maps from 71 samples, a parameter for the lipid to protein ratio was introduced involving the CH(2) symmetric stretch band with lipids as main contributors and the amide I band of proteins. As this parameter correlated with the grade of gliomas obtained from standard histopathological examination, it was applied to classify brain tissue sections based on IR spectroscopic mapping.     

On the mechanism of nanopore filling of SAPO-5 molecular sieve by nitrogen molecules

SAPO-5 molecular sieve was synthesized according to patent literature and characterized with X-ray diffraction, electron microscopy (SEM, TEM), and solid state magic angle spinning NMR spectroscopy. The material of particles in the micrometer region was found to consist of ca. 20 nm microcrystallites packed in mostly parallel orientation to ca. 200 nm sized agglomerates. The nitrogen adsorption isotherm was measured at 77.6 K over ca. 7 decades of pressure up to pore saturation. The course of the isotherm is interpreted to consist of filling of the nanopores (diameter, 0.73 nm) up to 2N(2)/unit cell, subsequent multilayer adsorption on the outer surface of the agglomerates, and, finally, pore condensation in the interparticle adsorption space. The nanopore adsorption can be quantitatively reproduced with the statistical mechanical model of a quasi one-dimensional lattice gas taking intermolecular interactions into account. The evaluated energy parameters are of physically reasonable magnitude and agree with literature data. The multilayer part of the adsorption isotherm can be well represented by the Brunauer-Emmett-Teller model yielding a specific outer space area (63 m(2) g(-)(1)) which is consistent with estimated geometrical and pore size analysis data.     

The effect of pressure on hydrogen transfer reactions with quinones

The effect of pressure on the oxidation of hydroarenes 3-9 with 2,3-dichloro-5,6-dicyano-1,4-quinone (DDQ; 1 a) or o-chloranil (10), leading to the corresponding arenes, has been investigated. The activation volumes were determined from the pressure dependence of the rate constants of these reactions monitored by on-line UV/Vis spectroscopic measurements in an optical high-pressure cell (up to 3500 bar). The finding that they are highly negative and only moderately dependent on the solvent polarity (DeltaV( not equal ) = -13 to -25 in MTBE and -15 to -29 cm(3) mol(-1) in MeCN/AcOEt, 1:1) rules out the formation of ionic species in the rate-determining step and is good evidence for a hydrogen atom transfer mechanism leading to a pair of radicals in the rate-determining step, as was also suggested by kinetic measurements, studies of kinetic isotope effects, and spin-trapping experiments. The strong pressure dependence of the kinetic deuterium isotope effect for the reaction of 9,10-dihydroanthracene 5/5-9,9,10,10-D(4) with DDQ (1 a) can be attributed to a tunneling component in the hydrogen transfer. In the case of formal 1,3-dienes and enes possessing two vicinal C--H bonds, which have to be cleaved during the dehydrogenation, a pericyclic hydrogen transfer has to considered as one mechanistic alternative. The comparison of the kinetic deuterium isotope effects determined for the oxidation of tetralin 9/9-1,1,4,4-D(4)/9-2,2,3,3-D(4)/9-D(12) either with DDQ (1 a) or with thymoquinone 1 c indicates that the reaction with DDQ (1 a) proceeds in a stepwise manner through hydrogen atom transfer, analogously to the oxidations of 1,4-dihydroarenes, whereas the reaction with thymoquinone 1 c is concerted, following the course of a pericyclic hydrogen transfer. The difference in the mechanistic courses of these two reactions may be explained by the effect of the CN and Cl substituents in 1 a, which stabilize a radical intermediate better than the alkyl groups in 1 c. The mechanistic conclusions are substantiated by DFT calculations.     

A vanadium-51 NMR study of the binding of vanadate and peroxovanadate to proteins

51V quadrupolar central transition NMR spectra of buffered (pH 7.6-8.0) solutions of bovine apo-transferrin (Tf) and bovine prostatic acid phosphatase (Pp) treated with vanadate show normal features (chemical shifts between -515 and -542 ppm) corresponding to the complexation of VO2+ to the Tf binding site and the Pp active centre, respectively. Addition of H2O2 leads to the temporary formation of complexed VO(O2)+ (delta approximately -595). Vanadate-dependent bromoperoxidase from the alga Ascophyllum nodosum exhibits an unusually high shielding both for the native (delta = -931) and the peroxo form (delta = -1135) of the enzyme. A resonance at -471 ppm is traced back to an inactive form with oxovanadium(V) in a trigonal-bipyramidal array.     

Measurement of PCDDs, PCDFs, and non-ortho-PCBs by comprehensive two-dimensional gas chromatography-isotope dilution time-of-flight mass spectrometry (GC x GC-IDTOFMS)

Comprehensive two-dimensional gas chromatography with isotope-dilution time-of-flight mass spectrometry (GC × GC-IDTOFMS) was used to measure polychlorinated dibenzo-p-dioxin (PCDD), polychlorinated dibenzofuran (PCDF), and coplanar polychlorinated biphenyl (cPCB) concentrations in ash, sediment, vegetation, and fish samples. The GC × GC capability was achieved by using a quad jet, dual stage, thermal modulator. Zone compression of the GC peaks from modulation resulted in a significant increase of the signal intensity over classical GC-IDTOFMS. The GC × GC column set used an Rtx-Dioxin 2 phase as the first dimension (¹D) and an Rtx-500 as the second dimension (²D). The chromatographic separation of the 17 PCDD/Fs and the 4 cPCBs was attained in ¹D except for 2,3,7,8-TCDD and CB126 for which deconvoluted ion currents (DIC) were required to be reported separately. The Rtx-500 phase separated the bulk matrix interfering compounds from the target analytes in ²D. The instrumental limit of detection (iLODs) was 0.5 pg for 2,3,7,8-TCDD. The calibration curves showed good correlation coefficients for all the compounds investigated in the concentration range of 0.5–200 pg. GC × GC-IDTOFMS results compared favorably to those from conventional isotope-dilution one-dimensional gas chromatography-high resolution mass spectrometry (GC-IDHRMS). The comprehensive mass analysis of the TOFMS further permitted the identification of other contaminants of concern in the samples.